The natural process of aging and the environment can lead to damage of the skin, affecting both its structure and functions. The skin keeps its condition through an inherent cycle of renewal, or natural exfoliation, that causes older, surface cells to drop off and allows fresher, newer skin to rise to the surface.
Acne is a follicular dermatosis. The comedo, which is the initial lesion of acne, resulting from the impaction of horny cells with the sebaceous follicle, develops in several stages. Primarily comedones develop first as microcomedones where the follicular ostium begins to be distended by horny material to form keratin plugs. The first visible lesion is the closed comedo or whitehead. Dilation of the follicular ostium by dark pigmented horny material marks the onset of an open comedo or blackhead. Subsequent rupture of closed or open comedones results in formation of secondary comedones which are generally larger and more irregularly shaped.
The bricks of the horny framework of comedones are corneocytes (i.e. individual dead skin cells) which are held together by a cement-like substance of extracellular lipids. Closed and open comedones develop into the nodules and pustules identified with inflammatory acne. Although there are multiple factors that appear to be operative in the pathogenesis of acne, it is the formation of keratin plugs that is the common denominator.
It is therefore apparent that a treatment directed at preventing or dissolving such keratin plugs (keratolysis) would reduce the compaction necessary to produce the comedo as well as helping to unseat existing comedones (comedolysis).
Acidic anti-acne agents are believed to cause a reduction in intercellular cohesion of the corneocytes, thereby dissolving the existing keratin plugs as well as preventing the formation of new ones. In order to best exert its keratolytic and comedolytic effect, it is desirable to deliver and deposit optimal concentrations of acidic anti-acne agents in the stratum corneum. Delivery of anti-acne agents through an aqueous system is beneficial for this purpose.
Acidic anti-acne agents are also believed to enhance the natural exfoliation process of the normal skin at relatively lower concentrations. It has been suggested that an appropriate cycle of efficient exfoliation helps the skin look and feel smoother, and reduces fine dry lines and provide even skin tone. Such refreshing feel of the skin is generally associated with an aqueous product. Thus, it is beneficial to combine the exfoliation benefit with refreshing feel attributed to an aqueous product.
However, most of these anti-acne agents are virtually insoluble in water, and thus difficult to incorporate these into aqueous systems. Furthermore, acidic anti-acne agents are most effective at low pH when a high concentration of free acid is present. It would thus be desirable to deliver the agent from an aqueous system at a low pH, at which the agent exists significantly in protonated form. This is particularly true for salicylic acid which is a well recognized anti-acne agent. Conventionally, high levels of alcohol and surfactants have been used to solubilize anti-acne agents. High levels of alcohol and surfactant can lead to compositions which are irritating when applied topically to the skin.
Consequently, it would be desirable to deliver acidic anti-acne agents in soluble form through a mild, yet refreshing aqueous system.